1. Field of the Invention
The present invention relates to a control device for an automatic transmission mounted in a vehicle such as a car or the like, and particularly to an automatic transmission control device for performing gearshift control by using a motor.
2. Description of the Related Art
In general, a vehicle such as a car or the like which has an automatic transmission mounted therein uses an engine as a driving power source, and transmits the driving power generated by the engine through the automatic transmission to wheels, whereby the vehicle can run. A start clutch is provided in the automatic transmission, and when it is necessary to transmit the driving power transmitted from the engine to a gear mechanism, the start clutch is engaged with the gear mechanism. Conversely, when it is unnecessary to transmit the driving power to the gear mechanism, the start clutch is disengaged from the gear mechanism. The control of the engagement/disengagement of the start clutch is executed by a clutch control unit.
Here, when the engaging force of the clutch is unstable, the driving power transmitted from the engine to the gear mechanism becomes unstable, and finally the driving power transmitted to the wheels becomes unstable. Therefore, this makes the traveling state of the vehicle unstable, and it makes a driver feel uncomfortable. As described above, in order to keep the traveling state of the vehicle stable, the start clutch is required to precisely control the engaging force thereof.
There is known an automatic transmission in which the transmission of the driving power from the engine to the gear mechanism is executed by the start clutch as described above. In the automatic transmission having the start clutch, a dry single plate type start clutch is provided with an actuator, and the actuator changes the stroke amount of the start clutch to thereby adjust the clutch engaging force. When the automatic transmission is configured so that a motor is used as the actuator and the rotational angle of the motor is proportional to the stroke amount of the start clutch, it is required to precisely adjust the torque amount of the motor in order to adjust the engaging force of the start clutch. The motor torque is proportional to the amount of current flowing in the motor, and thus in order to enhance the control precision of the motor torque, it is required to enhance the current control precision of the motor (for example, see JP-A-2002-81472).
On the other hand, it is general that the current of a motor is detected by inserting a current detecting resistor into a bus. However, the motor current contains a higher harmonic component which is six times as high as the operating frequency, and the current value to be detected may be dispersed in accordance with sampling timing. When the current value is dispersed, a result of current feedback control becomes unstable. In order to prevent this problem, there has been proposed a technique of generating a interrupting signal every 60° in electrical angle and calculating active current and reactive current every interrupting timing or conducting moving average on current values within a period of 60° in electrical angle, whereby the higher harmonic component is removed and the stability of the current feedback control is enhanced (for example, see JP-A-2004-282969).
Furthermore, as another technique of detecting the current of a motor, there has been proposed a technique of using a brushless DC motor of a 120° rectangular wave energizing system and detecting energizing current of coils of respective phases of the brushless DC motor every signal switching timing of plural hall sensors for detecting the position of a rotor of the brushless DC motor with respect to a stator of the brushless DC motor, thereby suppressing the dispersion of the current value (for example, see JP-A-2000-166277).
However, in the technique disclosed in JP-A-2004-282969, no attention is paid to a case where the coils of the respective phases of the motor are dispersed in resistance, etc. Accordingly, when a current detection value when the coils of the respective phases of the motor are dispersed in resistance is used for feedback control, dispersion of current is increased as a control result.
Here, this problem will be described in detail.
FIG. 14 is a diagram showing a behavior when the coil resistances of the respective phases of the motor are dispersed from one another, and shows a current feedback control result when current is sampled at an edge timing of the hall sensor. In this case, a response when the U-phase coil, a V-phase coil and a W-phase coil are set to 50 mΩ, 60 mΩ, 40 mΩ in resistance will be described.
In FIG. 14, current is made to flow from the U-phase to the V-phase for the period from 0° to 60° in electrical angle, and thus the coil resistance is set to 110 mΩ. Subsequently, current is made to flow from the U-phase to the W-phase for the period from 60° to 120° in electrical angle, and thus the coil resistance is set to 90 mΩ. Subsequently, current is made to flow from the V-phase to the W-phase for the period from 120° to 180° in electrical angle, and thus the coil resistance is set to 100 mΩ. Subsequently, current is made to flow from the V-phase to the U-phase for the period from 180° to 240° in electrical angle, and thus the coil resistance is set to 110 mΩ. Subsequently, current is made to flow from the W-phase to the V-phase for the period from 240° to 300° in electrical angle, and thus the coil resistance is set to 90 mΩ. Subsequently, current is made to flow from the W-phase to the V-phase for the period from 300° to 360° in electrical angle, and thus the coil resistance is set to 100 mΩ. As in the case of the period from 0° to 60° in electrical angle, current is made to flow from the U-phase to the V-phase for the period from 360° to 420° in electrical angle, and thus the coil resistance is set to 110 mΩ. As described above, three resistance values of 110 mΩ, 90 mΩ and 100 mΩ are provided as the value of the coil resistance, and these three resistance values are successively repeated.
Furthermore, in the current feedback control, current is sampled at every timing of 60° electrical angle like 0°, 60°, 120° in electrical angle, and an instruction voltage, that is, a next instruction voltage subsequent to the sampling timing of the current is calculated by using the sampled current value. That is, current is sampled every 60° electrical angle, and instruction duty is renewed. A calculating equation executed every 60° electrical angle can be represented by the following equations (1) and (2) when the dispersion of the coil resistance is represented by K. However, these equations are examples, and thus the present invention is not limited to these equations.Next instruction voltage=present instruction voltage+(target current−detected current)×K   (1)Instruction duty=next instruction voltage/power source voltage×100   (2)
Here, a calculating method for the current feedback control when the target current is set to 30A and K is equal to 0.1 will be described.
First, the instruction voltage 2.64(V) is set for a period till the electrical angle of 0°, and the coil resistance is equal to 100 mΩ, so that the motor current when the electrical angle is equal to zero is equal to 26.4A. At this time, from the equation (1)Next instruction voltage=2.64+(30.0−26.4)×0.1=3.00VAccordingly, current is made to flow into the motor while the instruction voltage for the period from 0° to 60° in electrical angle is equal to 3.00(V).
(State 1) Current is made to flow from the U-phase to the V-phase for the period from 0° to 60° in electrical angle, and thus the total coil resistance is equal to 110 mΩ. The instruction voltage is set to 3.00(V) as a calculation result of the current feedback, and thus the motor current at the electrical angle of 60° is equal to 27.3A.
Next, from the equation (1), the instruction voltage for the period from 60° to 120° in electrical angle is represented as follows:Next instruction voltage=3.00+(30.0−27.3)×0.1=3.27VAccordingly, current is made to flow into the motor while the instruction voltage for the period from 60° to 120° in electrical angle is set to 3.27(V).
(State 2) Current is made to flow from the U-phase to the W-phase for the period from 60° to 120° in electrical angle, and thus the total coil resistance is equal to 90 mΩ. Since the instruction voltage is set to 3.27(V) as a current feedback calculation result, so that the motor current at the electrical angle of 120° is equal to 36.3A.
Next, from the equation (1), the instruction voltage for the period from 120° to 180° in electrical angle is represented as follows:Next instruction voltage=3.27+(30.0−36.3)×0.1=2.64VAccordingly, current is made to flow into the motor while the instruction voltage for the period from 120° to 180° in electrical angle is set to 2.64(V).
(State 3) Current is made to flow from the V-phase to the W-phase for the period from 120° to 180° in electrical angle, and thus the total coil resistance is equal to 100 mΩ. Since the instruction voltage is set to 2.64(V) as a current feedback calculation result, so that the motor current at the electrical angle 180° is equal to 26.4A.
Next, from the equation (1), the instruction voltage for the period from 120° to 180° in electrical angle is represented as follows:Next instruction voltage=2.64+(30.0−26.4)×0.1=3.00VAccordingly, current is made to flow into the motor while the instruction voltage for the period from 180° to 240° is set to 3.00(V).
As described above, by repeating the states 1 to 3, the motor current has a dispersed response as shown in FIG. 14. Here, the dispersion (variation) width 61 of the motor current is equal to 36.3A−26.4A=9.9A.
As described above, in the conventional current feedback control, the instruction voltage of the present energization phase is calculated from the detection current at the preceding energization phase. Therefore, when the difference in coil resistance between the preceding energization phase and the present energization phase is large, there occurs a phenomenon that the dispersion of the motor current is increased.
The motor current and the motor torque amount are proportional to each other, and thus when the motor current is dispersed, the torque amount of the motor is also dispersed. As described above, in order to control the clutch engaging force with high precision, it is required to adjust the torque amount of the motor with high precision. Therefore, when current is dispersed and thus the torque amount is also dispersed, the engaging force of the clutch cannot be controlled with high precision. Accordingly, the limit value of the dispersion of the motor current is determined from the control precision of the clutch engaging force.
Here, it is generally known that the dispersion of current can be reduced by adjusting K described above. However, as shown in FIG. 15, when the dispersion of the motor current is reduced by setting K to a smaller value, there occurs a problem that a convergence time required for the current to reach motor target current is increased. When the follow-up performance to the current target value is lost, there occurs such a phenomenon that it becomes impossible to transmit torque when the motor current target value is increased to enhance the clutch engaging force in the control of the clutch engaging force.
Accordingly, in order to avoid the above problem, a predetermined threshold value is set for the convergence time to the motor target current. From FIG. 15, in the conventional current feedback control, the dispersion of the motor current is equal to δ1 when the convergence time is equal to a threshold value. As described above, in the conventional current feedback control, it is impossible to set a motor target current following time within the threshold value of the convergence time while the dispersion of the motor current is kept within a predetermined value.
Furthermore, in the control device of a DC motor of the 120° rectangular wave energizing system disclosed in JP-A-2000-166277, the dispersion of the current value is suppressed by detecting the motor current at the signal switching timing of the hall sensor. However, in this case, when the signal variation timing of the hall sensor is unequally angularly spaced with respect to “every 60° in electrical angle”, the current detection value is dispersed. Here, the response of the motor current is minimized at the switching time of the energization phase, and then gradually increases. Therefore, when the current detection timing is dispersed, gradually increasing current is sampled, so that the current detection value is dispersed. Actually, there are dispersion of installation of the hall sensor and characteristic dispersion, so that the signal variation interval of the hall sensor is unequal and thus the detection current value is dispersed. Accordingly, the current feedback control is unstable.
As described above, in the related arts, the feedback control precision is unstable, the current control precision is low and the clutch engaging force cannot be precisely controlled. Accordingly, the clutch engaging force is unstable, and the travel state of a vehicle is unstable.
For the purpose of suppressing the dispersion of the detection current value, oscillation of a current signal may be suppressed by increasing the time constant of a filter circuit. However, in this case, the variation of the motor current value is also slackened, and this causes a risk that instantaneous response performance is deteriorated.